The present invention relates to a control system for an internal combustion engine of electric ignition type, such as a gasoline engine, and more particularly, to an ignition timing control unit which is suitable for application to an automobile engine to prevent occurrence of irregular awkward running operation during acceleration.
In a vehicle, such as an automobile equipped with a gasoline engine, for example, when an accelerating operation is initiated by suddenly stepping on the accelerator pedal, there is produced in some cases a great change in running speed, that is, an acceleration surging, resulting in an awkward operation in which the speed fluctuates.
In order to suppress the occurrence of such awkward operation, there has hitherto been known a method in which engine torque is controlled by changing the ignition timing when an accelerating operation is detected, for instance, as disclosed in U.S. Pat. No. 4,799,469. Thus, according to this conventional method, a predetermined correction is constantly made on the standard ignition timing so as to suppress the change in the number of revolutions of the engine. This conventional method, however, gives no consideration to the fact that the change in the number of revolutions of the engine caused due to surging appears in an asymmetric form in some cases. This gives rise to a problem from the viewpoint of ensuring the satisfactory prevention of the irregular awkward operation at all times.
More specifically, in the above-described method, no consideration is give to a phenomenon in which, in some cases, the change in the number of revolutions of the engine appears in an asymmetric form with respect to the period and amplitude thereof in the increasing and decreasing directions. Accordingly, it is impossible with the above-described method to suppress the irregular operation satisfactorily when applied to an automobile or the like of the type that exhibits such asymmetric characteristic in the change in the number of revolutions of the engine.